Cathode-ray-tube-yoke combination with at least two spaced bodies of orangic thermoplastic material therebetween and a method of making said combination

ABSTRACT

Combination comprises a cathode-ray tube, a magnetic deflection yoke in operative releationship with the tube and at least two spaced bodies of organic thermoplastic material positioned between the yoke and the tube, the bodies filling less than 20 percent of the total volume in the space between the tube and the yoke. Method comprises placing a yoke in a predetermined spaced position with respect to a tube to provide a desired operative relationship therebetween. At least two substantially closed volumes are then defined between the yoke and the tube, the volumes enclosing less than 20 percent of the total volume in the spaced between the tube and the yoke. The defined volumes are substantially filled with heated liquid thermoplastic material, while the yoke and the tube are maintained at a temperature below about 50*C. The thermoplastic material is then permitted to cool and harden to a solid, which occurs at about 100*C.

Deal

Oct. 9, 1973 CATHODE-RAY-TUBE-YOKE COMBINATION WITH AT LEAST TWO SPACED BODIES OF ORANGIC THERMOPLASTIC MATERIAL THEREBETWEEN AND A METHOD OF MAKING SAID COMBINATION Inventor: Samuel Broughton Deal, Lancaster,

Assignee: RCA Corporation, New York, N.Y.

Filed: Aug. 21, 1972 Appl. No.: 282,272

US. Cl 178/7.8, 156/294, 264/262, 335/210 Int. Cl. H04n 5/64 Fleld of Search l78/7.8, 7.9; 335/210; 264/262; 156/294 References Cited UNITED STATES PATENTS 5/1972 Oberg ..178/7.8 2/1971 Brown 335/210 Primary Examiner-Howard W. Britton Attorney-Glenn H. Bruestle et a1.

[5 7] ABSTRACT Combination comprises a cathode-ray tube, a magnetic deflection yoke in operative releationship with the tube and at least two spaced bodies of organic thermoplastic material positioned between the yoke and the tube, the bodies filling less than 20 percent of the total volume in the space between the tube and the yoke.

Method comprises placing a yoke in a predetermined spaced position with respect to a tube to provide a desired operative relationship therebetween. At least two substantially closed volumes are then defined between the yoke and the tube, the volumes enclosing less than 20 percent of the total volume in the spaced between the tube and the yoke. The defined volumes are substantially filled with heated liquid thermoplastic material, while the yoke and the tube are maintained at a temperature below about 50C. The thermoplastic material is then permitted to cool and harden to a solid, which occurs at about 100C.

9 Claims, 5 Drawing Figures PATENIEDBBI n 3.764.740

SHEET 10F 2 CATHODE-RAY-TUBE-YOKE COMBINATION WITH AT LEAST TWO SPACED BODIES OF ORANGIC THERMOPLASTIC MATERIAL THEREBETWEEN AND A METHOD OF MAKING SAID COMBINATION BACKGROUND OF THE INVENTION This invention relates to a novel cathode-ray-tubeyoke combination wherein the yoke is attached on the tube with at least two spaced bodies of organic thermoplastic material, and to a novel method of making the combination.

A cathode-ray tube may use a magnetic deflection yoke mounted thereon to deflect the electron beams to scan a raster over the viewing-screen structure. The yoke may be attached on the neck of a cathode-ray tube with a body of cured polymeric material filling the volume between the yoke and tube, as described in US. Pat. No. 3,566,321 to M. G. Brown, Jr. Completely filling the volume between the tube and the yoke eliminates air circulation between the yoke and the tube and may result in a higher operating temperature of the combination and consequently a shorter operating life. Also, the filled volume provides an extremely rigid combination which may result in breakage of the yoke or tube, particularly under extreme environmental conditions such as low temperature. In addition, where the filled volume is large, an uneconomical amount of material may be required.

In one prior method of making a yoke-tube combination, a polymeric material is poured into the space between a positioned, operative yoke and tube and allowed to cure. Since, during the curing of the polymeric material, the yoke may move from the desired operative position on the tube, a retest after curing is desirable. Because a long curing time of about 48 hours is required, the combination must be removed from the test set to allow curing. Then after the curing is complete the tube must be repositioned in the test set for retesting. This may result in an uneconomical method when processing large quantities of yoke-tube combinations.

SUMMARY OF THE INVENTION The novel combination comprises a cathode-ray tube, a magnetic deflection yoke in operative relationship with the tube and at least two spaced bodies of organic thermoplastic material positioned between the yoke and the tube, the bodies filling less than percent of the total volume in the space between the tube and the yoke. The spaced bodies of thermoplastic material', instead of eliminating air circulation between the yoke and the tube, permit air circulation between portions of the yoke and the tube, resulting in a cooler, more reliable operation of the combination. Also, the spaced bodies provide some flexibility in the combination permitting sufficient movement between the yoke and the tube to substantially eliminate breakage of the yoke or the tube when the combination is exposed to extreme environmental conditions such as low temperature.

The novel method comprises placing a yoke in a predetermined spaced position with respect to the tube to provide a desired operative relationship therebetween. At least two substantially closed volumes are then defined between the tube and the yoke, the volumes enclosing less than 20 percent of the total volume in the space between the tube and the yoke. An organic thermoplastic material is heated to form a liquid thereof, and the defined volumes between the yoke and the tube are substantially filled with the heated thermoplastic material, while the tube and the yoke are maintained at a temperature below about 50C. The thermoplastic material is then permitted to cool and harden to a solid, which occurs at about C. Since the heated thermoplastic material solidifies within 60 seconds and no curing is involved, the combination does not require retesting. The novel process permits economical mass processing of large quantities of combinations. The novel method is particularly adapted for preparing the novel combination described above.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial broken-away elevational view of a yoke-tube combination.

FIG. 2 is an enlarged broken-away sectional view of a portion of the yoke and tube shown in FIG. 1.

FIG. 3 is a sectional view of the yoke-tube combination of FIG. 1.

FIG. 4 is an enlarged broken-away sectional view of a portion of a further alternate yoke-tube combination.

FIG. 5 is a sectional view of the yoke-tube combination shown in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates an apertured-mask color television picture tube 20 comprising an evacuated glass envelope 21. The envelope 21 includes a faceplate panel 22, a funnel 23, and a neck 24. A three-color-phosphorviewing-screen structure 25 is supported on the inner surface 26 of the faceplate panel 22. An electron-gun assembly 27 positioned in the neck 24 includes three electron guns (not shown), one for each of the three color phosphors on the viewing-screen structure 25. An apertured mask 28 is positioned in the envelope 21 adjacent the viewing-screen structure 25. The electrongun assembly 27 is adapted to project three electron beams through the apertured mask 28 to strike the viewing-screen structure 25.

A magnetic deflection yoke 29 is positioned adjacent the envelope 21 near the intersection of the funnel 23 and neck 24. The surface of the yoke 29 adjacent the surface of the tube 20 is defined to be the confronting surface of the yoke 29, and similarly the complementary surface of the tube 20 adjacent the yoke 29 is defined to be the confronting surface of the tube 20. The space 39 between the yoke-confronting surface and the tube-confronting surface is defined to contain the total volume between the yoke and the tube. The yoke 29 is fixed in place on the tube 20 by spaced bodies of solid organic thermoplastic material, which will be described in the specific examples. The yoke 29 may also include an auxiliary electromagnet or permanent magnet means such as a convergence or purity device (not shown) and terminal connection means (not shown).

EXAMPLE 1 FIGS. 2 and 3 illustrate a yoke 29, catalog No. XD-4503A distributed by RCA Corp., Indianapolis, Ind., attached on an RCA C76072 color television picture tube 20. The yoke 29 comprises a housing 31, a core 32, and windings 33. The yoke 29 is fixed on the tube by three spaced bodies 30 of solid organic thermoplastic material. The preferred thermoplastic material is an organic hot-melt thermoplastic adhesive material. Suitable materials and melting temperatures are described in Table I.

The bodies of organic thermoplastic material must remain solid at a yoke-operating temperature of about 100C and must melt below thetemperature at which damage to the yoke 29 or tube 20 would result, which occurs at about 150C, to permit economical salvage of component parts. Where the bodies 30 seal directly to the confronting surface (winding) of the yoke 20, it is preferred that the bodies 30 remain solid at about 125C. Thebodies 30 after hardening must also have good adhesion to the glass tube 20 and the yoke 29.

The tube 20 has a neck outside diameter 34 of about 0.937 and a funnel outside diameter 35 at the position of the large end of the yoke 29 of about 4.187 inches. The yoke 29 has an inside diameter 36 of about 1.187 inches at the small end and an inside diameter 37 of about 4.437 inches at the large end. The length 38 of the yoke is about 2.5 inches measured along the confronting surface of the yoke 20. The difference between the inside diameter of the yoke 29 and the outside diameter of the tube 20 provides a space 39 of about 0.050 to 0.150 inch between the tube 20 and the yoke 29 with the yoke and tube in a concentric position. A minimum space 39 of about 0.045 inch is required to permit X and Y translation of the yoke 29 on the tube 20 as shown in FIG. 1 during establishment of the desired operative relationship.

The bodies 30 of organic thermoplastic material are in the space between the yoke 29 and the tube 20. In one form, the bodies 30 comprise three strips of thermoplastic material substantially parallel to the axis of the tube and substantially equally-spaced on the periphery of the tube. It is preferred that three bodies are used for the catalog No. XD-4503A toroidal yoke 29 previously described. Table 11 gives the physical dimensions of each body of material. The confronting surface of the yoke 29 is empirically determined to be about square inches. Since the confronting surface of the yoke 29 is complementary to that of the tube 20, the confronting surface of the tube is also about 15 square inches. With three bodies of thermoplastic material of the size given in Table II, about 10 percent of the total volume in the space 39 between the yoke 29 and tube is filled. This leaves about 90 percent of the total volume in the space 39 unfilled and provides for air circulation between portions of the tube 20 and the yoke 29, which results in a cooler operation of the yoke and the tube.

EXAMPLE 2 This Example is the same as Example 1 except that the bodies 30 of thermoplastic material may be of a second size as given in Table II. With three bodies 30 of the second size, about 16 percent of the total volume in the space 39 is filled.

EXAMPLE 3 FIGS. 4 and 5 illustrate a saddle-type yoke 29a, catalog No. XD3696-I-I5 marketed by RCA Corp., lndianapolis, Ind., attached on an RCA XP22 color television picture tube 20a with four spaced bodies 40 of thermoplastic material. Important differences between Examples 1 and 3 are in the size of the yoke and tube and in the use of a saddle-type yoke. The embodiment of Examples 1 and 2 is known as a small-neck tube 20, and the embodiment of Example 3 is know as a large-neck tube 20a.

The tube 20a has a neck outside diameter 41 of about 1.625 inches and a funnel outside diameter 42 at the position of the large end of the yoke 29a of about 6.500 inches. The yoke 29a has an inside diameter 43 of about 1.875 inches at the small end and an inside diameter 44 of about 7.000 inches at the large end. The length 45 of the yoke 29a is about 4.250 inches measured along the inside confronting surface. The space 46 between the yoke 29a and the tube 20a is substantially uniform. The actual space 46 between the yoke 29a and the tube 20a in an operative relationship may be in the range of about 0.150 to 0.350 inch when measured with the tube 20a and yoke 29a in a concentric orientation. The confronting surface of the yoke 29a is empirically determined to have an area of about 50.25 square inches.

FIG. 5 illustrates the position of the four spaced bodies 40 of solid thermoplastic material. The size of each of the bodies 40 is given in Table I. The catalog No. XD3696-I-I5 saddle yoke includes a horizontal winding adjacent the tube 29a. The horizontal winding includes four groups 47 of wires substantially parallel to the longitudinal axis of the tube and substantially conforming to the confronting surface of the yoke 29a. The groups 47 are connected in pairs at the front and rear of the yoke 29a to form the horizontal windings. It is preferred that each of the four spaced bodies 40 of thermoplastic material is positioned between the yoke 29a and the tube 20a substantially centered on each of the four wire groups 47 as shown in FIG. 5. This provides for uniform movement of the yoke 29a with respect to the tube to compensate for extreme temperature variations. With four strips of thermoplastic material of the dimensions given in Table II, about 14 percent of the total volume in the space 46 is filled. This leaves about 86 percent of the total volume in the space 46 unfilled providing increased heat radiation from the combination to air in the unfilled space.

The novel method of attaching the yoke on the tube comprises placing the yoke 29 in a predetermined spaced position with respect to the tube 20 to provide a desired operative relationship therebetween. Operative relationship is defined to mean the position of the yoke relative to the tube that is required for the operation of the combination of a particular tube and a matching yoke in a television receiver.

The operative relationship may be established by generally positioning the yoke 29 adjacent the tube 20 and spaced within a desired tolerance. This operative relationship is generally used where the operation of the tube and yoke is adjustable by dynamic convergence circuitry. The operative relationship may also be established by temporarily positioning the yoke 29 on the tube 20, operating the tube 20 and yoke 29, and adjusting the position of the yoke 29 relative to the tube 20 while continuing to operate the combination until the desired operative relationship is established. In adjusting the combination, the yoke 29 can be moved axially in the direction Z, moved traversely in the directions X and Y, rotated in the direction R, or tilted in the direction T with respect to the axis of the tube as shown by the directional arrows in FIG. 1. This operative relationship is generally used where no dynamic convergence, or simplified dynamic convergence, circuitry is used.

After the operative relationship of the yoke 29 and tube 20 is established, at least two substantially closed volumes are defined in the space 39 between the yoke and the tube, the defined volumes enclosing less than 20 percent of the total volume in the space 39. The size of the preferred volumes is equal to the sizes of the bodies given in Table II.

ln the preferred method, the volumes are defined by positioning six pieces of foam silicone rubber strips 49 (shown in FIG. 2) on the inside surface of the yoke 29 or on the outside surface of the tube 20. The strips 49 are positioned substantially parallel to the longitudinal axis of the tube 20 and are equally spaced in pairs around the periphery of the outside of the tube 20 or the inside of the yoke 29. The pairs of strips 49 are spaced a distance apart equal to the desired width of the bodies 33 given in Examples 1 and 2. Since the foam strips 49 are compressible, they satisfactorily fill the space 39 between the yoke and tube at all times; and, since they are sufficiently flexible, they permit adjustment of the yoke and tube within the described adjustment range. The foam strips 49 are selected to be of an uncompressed thickness equal to the maximum possible spacing obtainable within the described adjustment range. It is preferred that the strips are i-inch wide. rz-inch thick, equal to the length of the yoke and compressible to a thickness of about one-sixteenth inch.

The strips 49 may be removed or retained in place after the bodies 30 of thermoplastic material have solidified. Since the strips 49 are of foam silicone rubber, they do not adhere to the bodies 30 of thermoplastic material and may be removed. If it is desired to remove the strips, it is preferred that the strips 49 are left longer than required with the longer ends temporarily attached to the yoke. For easy removal, the strips 49 may also be formed with end tabs. When the means for defining the volumes is retained with the combination for the life of the combination, adhesive-backed polyurethane foam tape may be used in place of the silicone foam strips. The adhesive backing permits retention of the foam tape in the desired position. But, since the thermoplastic material adheres to this tape, it is very difficult to remove after the bodies are formed.

A thermoplastic material, as previously described in Examples 1 and 2, is heated to a temperature in the range of about 375 to 425 F to form a liquid thereof. With the tube in the desired operative relationship, the defined volumes are substantially filled with the heated liquid thermoplastic material. During the filling step, the tube and the yoke are maintained at a temperature below about 50C. In a preferred method of filling the defined volumes, a plurality of masses of the heated liquid thermoplastic material are injected into the space 39 between the positioned yoke 29 and the tube 20 with the masses contacting less than 20 percent of the total confronting surfaces between the yoke 29 and the tube 20 and filling less than 20 percent of the total volume in the space between the yoke 29 and the tube 20.

With the spacing between the tube 20 and the yoke 29 in the range of about 0.062 to 0.250 inch, it is preferred to inject the liquid thermoplastic material at a rate of about 1 to 1.75 cubic inches per second.

The masses of liquid thermoplastic are permitted to solidify by allowing heat to be conducted to the positioned yoke and tube, the masses of the material cooling and hardening to a solid to form spaced bodies 30 between the yoke 29 and the tube 20. During the hardening, the yoke and tube are maintained at a temperature below C. The thermoplastic material hardens by physical change only, and no curing takes place.

The cooling and hardening of the masses of thermoplastic material to form bodies 30 thereof occur at least in part during the filling of the defined volumes with liquid thermoplastic material. The first-injected liquid thermoplastic material cools and hardens first, and the later-in-jected thermoplastic material progressively cools and hardens after the first-injected material has hardened. In practice, the temperature of the liquid thermoplastic material can be controlled for a particular matching yoke and tube combination such that the first-injected thermoplastic material hardens at about the opposite end of the yoke from the injection position. This eliminates the need to provide means to prevent the material from flowing beyond the end of the yoke 29. Of course, adhesive-backed foam tape could be easily positioned at one end of each of the body channels to fully define the end position of the bodies 30 prior to filling the volumes.

The cooling of the thermoplastic material substantially occurs by conduction to the tube 20 and the yoke 29. After the operative relationship of yoke 29 and tube 20 is established, the yoke temperature is about 50 C and the tube temperature is about 30 C. With the yoke 29 and tube 20 at these temperatures, the total hardening time is about 30 to seconds for the embodiment described in Example 1 and shown in FIGS. 2 and 3.

The novel method of making Example 3 is the same as that used in making Examples I and 2 except that there are four bodies 40, and the size of each of the bodies is larger as required for support of the larger yoke 29a. For the combination of Example 3, four pairs of foam tape (not shown) define volumes centered on the four wire groups 47. The defined volumes are equal to the sizes of the bodies given in Table II.

General Considerations and Alternatives The spaced bodies of thermoplastic material must leave sufficient volume in the space between the tube and the yoke unfilled to permit air circulation between the yoke and the tube. In addition, the bodies must also have a minimum width-to-thickness ratio to provide sufficient rigidity of the yoke on the tube. In practice, it is preferred to attach the yoke with a spacing less than 0.25 inch. At a spacing range of 0.0625 to 0.250 inch, the minimum width of each strip is about 0.20 inch, and the maximum width of each strip is about 0.500 inch. It is preferred that the width of each strip be about double the strip thickness. For any given strip width, the uncovered percentage of the total confronting surfaces is substantially equal to the unfilled percentage of the total volume in the space between the yoke and the tube.

The liquid thermoplastic may be injected into the space 39, without means to define the volumes, in the form of a bead directed to flow and harden in bodies 30 of width substantially as described in Example I. This is difficult to accomplish consistently, and it is preferred that either temporary or permanent means be provided to define the volume of the bodies 30 of thermoplastic material.

The means used to define the volumes must be flexible (compressible and expandable) to permit ease of movement of the yoke 29 with respect to the tube 20, as previously described. The means must expand and contract to continually define the volumes during the establishment of the operative relationship described. For example, when the yoke 29 is moved in the direction Y (shown in FIG. 1), the means used to define the volumes must expand on one side of the tube 20 and contract on the opposite side of the tube 20 to fill the space 39 between the yoke 29 and the tube 20 on both sides of the tube 20. Generally, the expansion required is from about 0.062 to 0.500 inch.

Although the fixturing means for defining the sidewalls for each of the bodies of thermoplastic material is disclosed to be a silicone rubber tape or a polyurethane foam tape, a smooth finish, small rubber tubing of neoprene rubber, butyl rubber, or polyethylene may also be used. A preferred tubing is marketed by Arthur H. Thomas, Philadelphia, Pa., as smooth finish, extruded, thin wall, black rubber tubing. The tubing is available in 3/16,0D X 1/16 wall thickness, 1 OD by 1/16 wall thickness, and 5% OD by l/32 wall thickness. In using the rubber tubing to define the volumes, rubber tubing (of a diameter greater than the space 39 or 46) is placed on the tube in the same position as previously described for the foam tape. The tubing is compressible and expands and compresses to fill the variable space between the yoke and tube. A preferred method of positioning the tubing is to extend the ends beyond the ends of the yoke and temporarily attach them to the yoke. The smooth finish of the tubing substantially prevents the thermoplastic material from adhering to the tubing. The extended ends permit the tubing to be pulled out after the bodies of thermoplastic material have hardened.

Although the spaced bodies of thermoplastic mate-' rial are described to be strips substantially parallel to the longitudinal axis of the tube, other body configurations are possible. For example, the strips can be segmented and staggered. Also, bodies of about one half inch in diameter could be positioned between the yoke and tube in any convenient arrangement. One arrangement may be to position three one-half-inch-diameter bodies at each end of a toroidal yoke substantially uniformly spaced around the periphery thereof. Whatever the arrangement selected, the bodies must be spaced and must fill less than twenty percent of the total volume in the space 39 or 46.

When the yoke 29 includes a housing on the inside surface, the housing can include thin flexible members over the length of the housing to substitute for the tape strips 49 described. These members could be accordioned or folded to permit movement of the yoke 29 on the tube 29 within the range described, while continuously providing defined volumes for the casting of each of the spaced bodies 30 or 40. This would eliminate the separate strips 49, providing for further economy in the novel method.

The hardening time for the bodies of organic thermoplastic material can also be accelerated by forced cooling. In a preferred method of cooling, an air stream at a temperature of about 40 to 45 C is directed to flow through the unfilled portion between the combination. Forced cooling reduces hardening time in the order of about 2:1 or 3:1 of that normally required. This permits hardening in about to 30 seconds, permitting increased production rate and resulting in subsequent economies.

TABLE I Melting Material Marketed B Temperature Versalon 1 138 General Mil s Chemical C Co., Minneapolis, Minn. Versalon 1165 134C TABLE II Str' Stri Strip Strip Surface Example Wici ih Thickness Lengt Area No. (inches) (inches) (inches) (square inches) 1 0.20 0.05 2.50 0.024 2 0.35 0.15 2.50 0.131 3 0.35 0.25 4.25 0.371

I claim:

1. In combination,

a. a cathode-ray tube,

b. a magnetic deflection yoke in operative relationship with said tube c. and at least two spaced solid bodies of organic thermoplastic material positioned between said yoke and said tube, said bodies filling less than 20 percent of the total volume in the space between said yoke and said tube.

2. The combination defined in claim 1 wherein each of said bodies is about 0.20 to 0.500 inch wide by 0.650 to 0.375 inch thick by 2.500 to 4.250 inches long.

3. The combination defined in claim 1 wherein said yoke includes four groups of wires substantially parallel to the longitudinal axis of said tube, said bodies comprising a strip of material positioned between each of said groups and said tube.

4. The combination defined in claim 1 including (1. means between said yoke and said tube defining the position of each of said bodies.

5. The combination defined in claim 1 wherein said organic thermoplastic material is a hot-melt adhesive which is solid at a temperature of about 100C and melts at about C.

6. The combination defined in claim 5 wherein said spaced bodies of organic material provide movement of said yoke with respect to said tube during temperature variations.

7. A method of fixedly attaching a yoke in a predetermined, spaced position on a cathode-ray tube comprising the steps of a. placing said yoke in said predetermined, spaced position with respect to said tube to provide a desired operative relationship therebetween,

b. defining at least two substantially closed volumes between said yoke and said tube, said volumes enclosing less than 20 percent of the total volume in the space between said yoke and said tube,

0. heating an organic thermoplastic material to form a liquid thereof,

(1. substantially filling said defined volumes with heated liquid thermoplastic material,

e. during step (d) maintaining said yoke and tube at a temperature below about 50C -f. and then permitting said thermoplastic material to cool and harden to a solid which occurs at about 100C.

8. The method defined in claim 7 wherein step (f) includes hardening by directing cooling air between said yoke and said tube, said hardening occurring in less than 30 seconds.

9. The method defined in claim 7 wherein said organic thermoplastic material is a hot-melt adhesive which is solid at a temperature of about 100C and melts at about 150C. 

2. The combination defined in claim 1 wherein each of said bodies is about 0.20 to 0.500 inch wide by 0.650 to 0.375 inch thick by 2.500 to 4.250 inches long.
 3. The combination defined in claim 1 wherein said yoke includes four groups of wires substantially parallel to the longitudinal axis of said tube, said bodies comprising a strip of material positioned between each of said groups and said tube.
 4. The combination defined in claim 1 including d. means between said yoke and said tube defining the position of each of said bodies.
 5. The combination defined in claim 1 wherein said organic thermoplastic material is a hot-melt adhesive which is solid at a temperature of about 100*C and melts at about 150*C.
 6. The combination defined in claim 5 wherein said spaced bodies of organic material provide movement of said yoke with respect to said tube during temperature variations.
 7. A method of fixedly attaching a yoke in a predetermined, spaced position on a cathode-ray tube comprising the steps of a. placing said yoke in said predetermined, spaced position with respect to said tube to provide a Desired operative relationship therebetween, b. defining at least two substantially closed volumes between said yoke and said tube, said volumes enclosing less than 20 percent of the total volume in the space between said yoke and said tube, c. heating an organic thermoplastic material to form a liquid thereof, d. substantially filling said defined volumes with heated liquid thermoplastic material, e. during step (d) maintaining said yoke and tube at a temperature below about 50*C f. and then permitting said thermoplastic material to cool and harden to a solid which occurs at about 100*C.
 8. The method defined in claim 7 wherein step (f) includes hardening by directing cooling air between said yoke and said tube, said hardening occurring in less than 30 seconds.
 9. The method defined in claim 7 wherein said organic thermoplastic material is a hot-melt adhesive which is solid at a temperature of about 100*C and melts at about 150*C. 